/*
 * Copyright (C) 2008 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.primitives;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkElementIndex;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkPositionIndexes;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;

import java.io.Serializable;
import java.util.AbstractList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.RandomAccess;
import javax.annotation.CheckForNull;

/**
 * Static utility methods pertaining to {@code char} primitives, that are not already found in
 * either {@link Character} or {@link Arrays}.
 *
 * <p>All the operations in this class treat {@code char} values strictly numerically; they are
 * neither Unicode-aware nor locale-dependent.
 *
 * <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/PrimitivesExplained">primitive utilities</a>.
 *
 * @author Kevin Bourrillion
 * @since 1.0
 */
@GwtCompatible(emulated = true)
@ElementTypesAreNonnullByDefault
public final class Chars
{
    private Chars()
    {
    }

    /**
     * The number of bytes required to represent a primitive {@code char} value.
     *
     * <p><b>Java 8 users:</b> use {@link Character#BYTES} instead.
     */
    public static final int BYTES = Character.SIZE / Byte.SIZE;

    /**
     * Returns a hash code for {@code value}; equal to the result of invoking {@code ((Character)
     * value).hashCode()}.
     *
     * <p><b>Java 8 users:</b> use {@link Character#hashCode(char)} instead.
     *
     * @param value a primitive {@code char} value
     * @return a hash code for the value
     */
    public static int hashCode(char value)
    {
        return value;
    }

    /**
     * Returns the {@code char} value that is equal to {@code value}, if possible.
     *
     * @param value any value in the range of the {@code char} type
     * @return the {@code char} value that equals {@code value}
     * @throws IllegalArgumentException if {@code value} is greater than {@link Character#MAX_VALUE}
     *                                  or less than {@link Character#MIN_VALUE}
     */
    public static char checkedCast(long value)
    {
        char result = (char) value;
        checkArgument(result == value, "Out of range: %s", value);
        return result;
    }

    /**
     * Returns the {@code char} nearest in value to {@code value}.
     *
     * @param value any {@code long} value
     * @return the same value cast to {@code char} if it is in the range of the {@code char} type,
     * {@link Character#MAX_VALUE} if it is too large, or {@link Character#MIN_VALUE} if it is too
     * small
     */
    public static char saturatedCast(long value)
    {
        if (value > Character.MAX_VALUE)
        {
            return Character.MAX_VALUE;
        }
        if (value < Character.MIN_VALUE)
        {
            return Character.MIN_VALUE;
        }
        return (char) value;
    }

    /**
     * Compares the two specified {@code char} values. The sign of the value returned is the same as
     * that of {@code ((Character) a).compareTo(b)}.
     *
     * <p><b>Note for Java 7 and later:</b> this method should be treated as deprecated; use the
     * equivalent {@link Character#compare} method instead.
     *
     * @param a the first {@code char} to compare
     * @param b the second {@code char} to compare
     * @return a negative value if {@code a} is less than {@code b}; a positive value if {@code a} is
     * greater than {@code b}; or zero if they are equal
     */
    public static int compare(char a, char b)
    {
        return a - b; // safe due to restricted range
    }

    /**
     * Returns {@code true} if {@code target} is present as an element anywhere in {@code array}.
     *
     * @param array  an array of {@code char} values, possibly empty
     * @param target a primitive {@code char} value
     * @return {@code true} if {@code array[i] == target} for some value of {@code i}
     */
    public static boolean contains(char[] array, char target)
    {
        for (char value : array)
        {
            if (value == target)
            {
                return true;
            }
        }
        return false;
    }

    /**
     * Returns the index of the first appearance of the value {@code target} in {@code array}.
     *
     * @param array  an array of {@code char} values, possibly empty
     * @param target a primitive {@code char} value
     * @return the least index {@code i} for which {@code array[i] == target}, or {@code -1} if no
     * such index exists.
     */
    public static int indexOf(char[] array, char target)
    {
        return indexOf(array, target, 0, array.length);
    }

    // TODO(kevinb): consider making this public
    private static int indexOf(char[] array, char target, int start, int end)
    {
        for (int i = start; i < end; i++)
        {
            if (array[i] == target)
            {
                return i;
            }
        }
        return -1;
    }

    /**
     * Returns the start position of the first occurrence of the specified {@code target} within
     * {@code array}, or {@code -1} if there is no such occurrence.
     *
     * <p>More formally, returns the lowest index {@code i} such that {@code Arrays.copyOfRange(array,
     * i, i + target.length)} contains exactly the same elements as {@code target}.
     *
     * @param array  the array to search for the sequence {@code target}
     * @param target the array to search for as a sub-sequence of {@code array}
     */
    public static int indexOf(char[] array, char[] target)
    {
        checkNotNull(array, "array");
        checkNotNull(target, "target");
        if (target.length == 0)
        {
            return 0;
        }

        outer:
        for (int i = 0; i < array.length - target.length + 1; i++)
        {
            for (int j = 0; j < target.length; j++)
            {
                if (array[i + j] != target[j])
                {
                    continue outer;
                }
            }
            return i;
        }
        return -1;
    }

    /**
     * Returns the index of the last appearance of the value {@code target} in {@code array}.
     *
     * @param array  an array of {@code char} values, possibly empty
     * @param target a primitive {@code char} value
     * @return the greatest index {@code i} for which {@code array[i] == target}, or {@code -1} if no
     * such index exists.
     */
    public static int lastIndexOf(char[] array, char target)
    {
        return lastIndexOf(array, target, 0, array.length);
    }

    // TODO(kevinb): consider making this public
    private static int lastIndexOf(char[] array, char target, int start, int end)
    {
        for (int i = end - 1; i >= start; i--)
        {
            if (array[i] == target)
            {
                return i;
            }
        }
        return -1;
    }

    /**
     * Returns the least value present in {@code array}.
     *
     * @param array a <i>nonempty</i> array of {@code char} values
     * @return the value present in {@code array} that is less than or equal to every other value in
     * the array
     * @throws IllegalArgumentException if {@code array} is empty
     */
    public static char min(char... array)
    {
        checkArgument(array.length > 0);
        char min = array[0];
        for (int i = 1; i < array.length; i++)
        {
            if (array[i] < min)
            {
                min = array[i];
            }
        }
        return min;
    }

    /**
     * Returns the greatest value present in {@code array}.
     *
     * @param array a <i>nonempty</i> array of {@code char} values
     * @return the value present in {@code array} that is greater than or equal to every other value
     * in the array
     * @throws IllegalArgumentException if {@code array} is empty
     */
    public static char max(char... array)
    {
        checkArgument(array.length > 0);
        char max = array[0];
        for (int i = 1; i < array.length; i++)
        {
            if (array[i] > max)
            {
                max = array[i];
            }
        }
        return max;
    }

    /**
     * Returns the value nearest to {@code value} which is within the closed range {@code [min..max]}.
     *
     * <p>If {@code value} is within the range {@code [min..max]}, {@code value} is returned
     * unchanged. If {@code value} is less than {@code min}, {@code min} is returned, and if {@code
     * value} is greater than {@code max}, {@code max} is returned.
     *
     * @param value the {@code char} value to constrain
     * @param min   the lower bound (inclusive) of the range to constrain {@code value} to
     * @param max   the upper bound (inclusive) of the range to constrain {@code value} to
     * @throws IllegalArgumentException if {@code min > max}
     * @since 21.0
     */
    @Beta
    public static char constrainToRange(char value, char min, char max)
    {
        checkArgument(min <= max, "min (%s) must be less than or equal to max (%s)", min, max);
        return value < min ? min : value < max ? value : max;
    }

    /**
     * Returns the values from each provided array combined into a single array. For example, {@code
     * concat(new char[] {a, b}, new char[] {}, new char[] {c}} returns the array {@code {a, b, c}}.
     *
     * @param arrays zero or more {@code char} arrays
     * @return a single array containing all the values from the source arrays, in order
     */
    public static char[] concat(char[]... arrays)
    {
        int length = 0;
        for (char[] array : arrays)
        {
            length += array.length;
        }
        char[] result = new char[length];
        int pos = 0;
        for (char[] array : arrays)
        {
            System.arraycopy(array, 0, result, pos, array.length);
            pos += array.length;
        }
        return result;
    }

    /**
     * Returns a big-endian representation of {@code value} in a 2-element byte array; equivalent to
     * {@code ByteBuffer.allocate(2).putChar(value).array()}. For example, the input value {@code
     * '\\u5432'} would yield the byte array {@code {0x54, 0x32}}.
     *
     * <p>If you need to convert and concatenate several values (possibly even of different types),
     * use a shared {@link java.nio.ByteBuffer} instance, or use {@link
     * com.google.common.io.ByteStreams#newDataOutput()} to get a growable buffer.
     */
    @GwtIncompatible // doesn't work
    public static byte[] toByteArray(char value)
    {
        return new byte[]{(byte) (value >> 8), (byte) value};
    }

    /**
     * Returns the {@code char} value whose big-endian representation is stored in the first 2 bytes
     * of {@code bytes}; equivalent to {@code ByteBuffer.wrap(bytes).getChar()}. For example, the
     * input byte array {@code {0x54, 0x32}} would yield the {@code char} value {@code '\\u5432'}.
     *
     * <p>Arguably, it's preferable to use {@link java.nio.ByteBuffer}; that library exposes much more
     * flexibility at little cost in readability.
     *
     * @throws IllegalArgumentException if {@code bytes} has fewer than 2 elements
     */
    @GwtIncompatible // doesn't work
    public static char fromByteArray(byte[] bytes)
    {
        checkArgument(bytes.length >= BYTES, "array too small: %s < %s", bytes.length, BYTES);
        return fromBytes(bytes[0], bytes[1]);
    }

    /**
     * Returns the {@code char} value whose byte representation is the given 2 bytes, in big-endian
     * order; equivalent to {@code Chars.fromByteArray(new byte[] {b1, b2})}.
     *
     * @since 7.0
     */
    @GwtIncompatible // doesn't work
    public static char fromBytes(byte b1, byte b2)
    {
        return (char) ((b1 << 8) | (b2 & 0xFF));
    }

    /**
     * Returns an array containing the same values as {@code array}, but guaranteed to be of a
     * specified minimum length. If {@code array} already has a length of at least {@code minLength},
     * it is returned directly. Otherwise, a new array of size {@code minLength + padding} is
     * returned, containing the values of {@code array}, and zeroes in the remaining places.
     *
     * @param array     the source array
     * @param minLength the minimum length the returned array must guarantee
     * @param padding   an extra amount to "grow" the array by if growth is necessary
     * @return an array containing the values of {@code array}, with guaranteed minimum length {@code
     * minLength}
     * @throws IllegalArgumentException if {@code minLength} or {@code padding} is negative
     */
    public static char[] ensureCapacity(char[] array, int minLength, int padding)
    {
        checkArgument(minLength >= 0, "Invalid minLength: %s", minLength);
        checkArgument(padding >= 0, "Invalid padding: %s", padding);
        return (array.length < minLength) ? Arrays.copyOf(array, minLength + padding) : array;
    }

    /**
     * Returns a string containing the supplied {@code char} values separated by {@code separator}.
     * For example, {@code join("-", '1', '2', '3')} returns the string {@code "1-2-3"}.
     *
     * @param separator the text that should appear between consecutive values in the resulting string
     *                  (but not at the start or end)
     * @param array     an array of {@code char} values, possibly empty
     */
    public static String join(String separator, char... array)
    {
        checkNotNull(separator);
        int len = array.length;
        if (len == 0)
        {
            return "";
        }

        StringBuilder builder = new StringBuilder(len + separator.length() * (len - 1));
        builder.append(array[0]);
        for (int i = 1; i < len; i++)
        {
            builder.append(separator).append(array[i]);
        }
        return builder.toString();
    }

    /**
     * Returns a comparator that compares two {@code char} arrays <a
     * href="http://en.wikipedia.org/wiki/Lexicographical_order">lexicographically</a>; not advisable
     * for sorting user-visible strings as the ordering may not match the conventions of the user's
     * locale. That is, it compares, using {@link #compare(char, char)}), the first pair of values
     * that follow any common prefix, or when one array is a prefix of the other, treats the shorter
     * array as the lesser. For example, {@code [] < ['a'] < ['a', 'b'] < ['b']}.
     *
     * <p>The returned comparator is inconsistent with {@link Object#equals(Object)} (since arrays
     * support only identity equality), but it is consistent with {@link Arrays#equals(char[],
     * char[])}.
     *
     * @since 2.0
     */
    public static Comparator<char[]> lexicographicalComparator()
    {
        return LexicographicalComparator.INSTANCE;
    }

    private enum LexicographicalComparator implements Comparator<char[]>
    {
        INSTANCE;

        @Override
        public int compare(char[] left, char[] right)
        {
            int minLength = Math.min(left.length, right.length);
            for (int i = 0; i < minLength; i++)
            {
                int result = Chars.compare(left[i], right[i]);
                if (result != 0)
                {
                    return result;
                }
            }
            return left.length - right.length;
        }

        @Override
        public String toString()
        {
            return "Chars.lexicographicalComparator()";
        }
    }

    /**
     * Copies a collection of {@code Character} instances into a new array of primitive {@code char}
     * values.
     *
     * <p>Elements are copied from the argument collection as if by {@code collection.toArray()}.
     * Calling this method is as thread-safe as calling that method.
     *
     * @param collection a collection of {@code Character} objects
     * @return an array containing the same values as {@code collection}, in the same order, converted
     * to primitives
     * @throws NullPointerException if {@code collection} or any of its elements is null
     */
    public static char[] toArray(Collection<Character> collection)
    {
        if (collection instanceof CharArrayAsList)
        {
            return ((CharArrayAsList) collection).toCharArray();
        }

        Object[] boxedArray = collection.toArray();
        int len = boxedArray.length;
        char[] array = new char[len];
        for (int i = 0; i < len; i++)
        {
            // checkNotNull for GWT (do not optimize)
            array[i] = (Character) checkNotNull(boxedArray[i]);
        }
        return array;
    }

    /**
     * Sorts the elements of {@code array} in descending order.
     *
     * @since 23.1
     */
    public static void sortDescending(char[] array)
    {
        checkNotNull(array);
        sortDescending(array, 0, array.length);
    }

    /**
     * Sorts the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
     * exclusive in descending order.
     *
     * @since 23.1
     */
    public static void sortDescending(char[] array, int fromIndex, int toIndex)
    {
        checkNotNull(array);
        checkPositionIndexes(fromIndex, toIndex, array.length);
        Arrays.sort(array, fromIndex, toIndex);
        reverse(array, fromIndex, toIndex);
    }

    /**
     * Reverses the elements of {@code array}. This is equivalent to {@code
     * Collections.reverse(Chars.asList(array))}, but is likely to be more efficient.
     *
     * @since 23.1
     */
    public static void reverse(char[] array)
    {
        checkNotNull(array);
        reverse(array, 0, array.length);
    }

    /**
     * Reverses the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
     * exclusive. This is equivalent to {@code
     * Collections.reverse(Chars.asList(array).subList(fromIndex, toIndex))}, but is likely to be more
     * efficient.
     *
     * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
     *                                   {@code toIndex > fromIndex}
     * @since 23.1
     */
    public static void reverse(char[] array, int fromIndex, int toIndex)
    {
        checkNotNull(array);
        checkPositionIndexes(fromIndex, toIndex, array.length);
        for (int i = fromIndex, j = toIndex - 1; i < j; i++, j--)
        {
            char tmp = array[i];
            array[i] = array[j];
            array[j] = tmp;
        }
    }

    /**
     * Returns a fixed-size list backed by the specified array, similar to {@link
     * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
     * set a value to {@code null} will result in a {@link NullPointerException}.
     *
     * <p>The returned list maintains the values, but not the identities, of {@code Character} objects
     * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
     * the returned list is unspecified.
     *
     * @param backingArray the array to back the list
     * @return a list view of the array
     */
    public static List<Character> asList(char... backingArray)
    {
        if (backingArray.length == 0)
        {
            return Collections.emptyList();
        }
        return new CharArrayAsList(backingArray);
    }

    @GwtCompatible
    private static class CharArrayAsList extends AbstractList<Character>
            implements RandomAccess, Serializable
    {
        final char[] array;
        final int start;
        final int end;

        CharArrayAsList(char[] array)
        {
            this(array, 0, array.length);
        }

        CharArrayAsList(char[] array, int start, int end)
        {
            this.array = array;
            this.start = start;
            this.end = end;
        }

        @Override
        public int size()
        {
            return end - start;
        }

        @Override
        public boolean isEmpty()
        {
            return false;
        }

        @Override
        public Character get(int index)
        {
            checkElementIndex(index, size());
            return array[start + index];
        }

        @Override
        public boolean contains(@CheckForNull Object target)
        {
            // Overridden to prevent a ton of boxing
            return (target instanceof Character)
                    && Chars.indexOf(array, (Character) target, start, end) != -1;
        }

        @Override
        public int indexOf(@CheckForNull Object target)
        {
            // Overridden to prevent a ton of boxing
            if (target instanceof Character)
            {
                int i = Chars.indexOf(array, (Character) target, start, end);
                if (i >= 0)
                {
                    return i - start;
                }
            }
            return -1;
        }

        @Override
        public int lastIndexOf(@CheckForNull Object target)
        {
            // Overridden to prevent a ton of boxing
            if (target instanceof Character)
            {
                int i = Chars.lastIndexOf(array, (Character) target, start, end);
                if (i >= 0)
                {
                    return i - start;
                }
            }
            return -1;
        }

        @Override
        public Character set(int index, Character element)
        {
            checkElementIndex(index, size());
            char oldValue = array[start + index];
            // checkNotNull for GWT (do not optimize)
            array[start + index] = checkNotNull(element);
            return oldValue;
        }

        @Override
        public List<Character> subList(int fromIndex, int toIndex)
        {
            int size = size();
            checkPositionIndexes(fromIndex, toIndex, size);
            if (fromIndex == toIndex)
            {
                return Collections.emptyList();
            }
            return new CharArrayAsList(array, start + fromIndex, start + toIndex);
        }

        @Override
        public boolean equals(@CheckForNull Object object)
        {
            if (object == this)
            {
                return true;
            }
            if (object instanceof CharArrayAsList)
            {
                CharArrayAsList that = (CharArrayAsList) object;
                int size = size();
                if (that.size() != size)
                {
                    return false;
                }
                for (int i = 0; i < size; i++)
                {
                    if (array[start + i] != that.array[that.start + i])
                    {
                        return false;
                    }
                }
                return true;
            }
            return super.equals(object);
        }

        @Override
        public int hashCode()
        {
            int result = 1;
            for (int i = start; i < end; i++)
            {
                result = 31 * result + Chars.hashCode(array[i]);
            }
            return result;
        }

        @Override
        public String toString()
        {
            StringBuilder builder = new StringBuilder(size() * 3);
            builder.append('[').append(array[start]);
            for (int i = start + 1; i < end; i++)
            {
                builder.append(", ").append(array[i]);
            }
            return builder.append(']').toString();
        }

        char[] toCharArray()
        {
            return Arrays.copyOfRange(array, start, end);
        }

        private static final long serialVersionUID = 0;
    }
}
